Tandem axle suspensions are available in the prior art and generally include a pair of heavy duty springs to resist movement of the axles in the vertical direction with respect to the frame of the vehicles. In addition, some suspension systems provide structure to help balance the load between the axles to thereby improve the braking characteristics and wheel contact resulting in a much safer and more comfortable ride. Applicant has designed and patented several of these systems, including U.S. Pat. Nos. 3,471,165 and 3,632,128, the disclosures of which are incorporated herein by reference. These patented suspension systems are highly successful and provide a pair of sandwich type heavy duty load springs which extend between torque beams and a compensator. In at least one of the embodiments of U.S. Pat. No. 3,632,128, a smaller sandwich type spring is mounted between vertical plates projecting upwardly from the torque beams, these springs being of reduced capacity and providing for translation of effective loading from one axle to the other.
Applicant's prior suspension systems are designed and manufactured to operate many hundreds of thousands of miles without any maintenance. However, when it eventually is necessary to perform an overhaul on these suspensions, the main springs must be removed and replaced. The effort required to replace the springs of applicant's prior art suspensions is significantly reduced over that of other prior art suspensions but still requires that the suspension be dismantled from the vehicle and disassembled, and the compensator at least partially disassembled. This procedure is relatively easy to perform and applicant's suspensions are significantly easier to maintain and substitute replacement springs than other prior art suspension systems.
To reduce even the small amount of time required in applicant's previous suspensions, applicant has developed a new suspension system which has a single heavy duty spring member which can be removed and replaced in only a fraction of the time required for other suspensions and which provides the same features of his prior art systems and more. Applicant's new suspension utilizes a central, horizontally disposed, principal load-bearing spring member which extends between two pivotally mounted torque beams. A smaller compensator is mounted to a trunnion shaft and includes a pair of sandwich type elastomer and steel plate springs extending between the compensator and the torque beams to dampen the deflection of the central spring. The capacity of the suspension and the degree of deflection may be adjusted by choosing the stiffness of springs used. Because the central spring is "free-floating" between the two pivotally mounted torque beams, it also helps balance an uneven loading between the axles along with the compensator assembly. An unbalanced load at one axle shifts the central spring and compensator assembly both to distribute the load evenly between the axles.
In a first embodiment, the central spring is mounted between the torque beams by a mounting stud at each torque beam which extends into an axial cylindrical opening extending the length of the spring. The axial opening also provides room for the expansion of the elastomer as it is compressed under load by the torque beams. Each end of the spring is fixed with respect to its adjacent torque beam except for distortion occurring in the elastomeric material. In the second embodiment, the ends of the spring are permitted to "float" or pivot within a limited range. In this embodiment, self lubricating, convex fiber blocks are positioned adjacent each spring end and a matching, concave fiber surface is affixed to each torque beam. Opposing U-shaped saddle brackets with an aligned arcuate slot and stop bolt secure each spring end to its adjacent torque beam so that the spring end may pivot with respect to the torque beam. Movement is limited however by the arcuate slot and stop bolt.
Applicant's principal central spring may be replaced merely by removing a pair of set screw stops, elevating the vehicle chassis and merely lifting the central spring means out from between two mounting studs and replacing it with a new one. The set screw stops prevent unintended removal or cocking of the central spring when the vehicle is jacked up for other purposes. In a second embodiment, two more bolts must be loosened, but it is still possible to replace the single principal spring without disassembling the suspension system, removing it from the vehicle, or even partial disassembly of the compensator.
Thus, applicant's suspension provides for quick and easy removal and replacement of the central, principal load-bearing spring and an increased ability to distribute an unbalanced load equally between the axles.